Servo control device of DC motor

ABSTRACT

At the time of controlling a servo mechanism, a servo control detects that the position of a driven body is in the steady judgment region of a target position and varies a control constant (PI value) in the steady judgment region, so it is made possible to reduce an oscillation of the driven body in the steady judgment region.

TECHNICAL FIELD

The present invention relates to a servo control device of a DC motorfor controlling an object to be controlled of a servomechanism forcontrolling a mechanical position or an angle, for example, an exhaustgas recirculation (hereinafter referred to as EGR) valve provided in arecirculation system of an exhaust gas, a throttle valve, an actuator ofa turbocharger and the like.

BACKGROUND ART

FIG. 1 shows a diagram in which a valve 11 of an EGR valve arranged inan exhaust gas return passage (c) for making an exhaust gas passage (a)of an engine E communicate with an intake gas passage (b) thereof is anobject to be controlled and in which a DC motor 21 is driven by theoutput of a control section 50 to control the opening of the valve 11.

FIG. 2 is a longitudinal cross sectional view to show a constitution ofthe EGR valve to which a servo control device is applied having a DCmotor 21 as a driving source. In FIG. 2, a reference numeral 1 denotes avalve body in which a passage communicating with the exhaust gas returnpassage (c) is disposed in a recirculation system of an exhaust gas.When the valve 11 is moved up as shown in the drawing, it is put intocontact with a seat 12 to close the exhaust gas return passage c andwhen the valve 11 is moved down, it is separated from the seat 12 toopen the exhaust gas return passage (c).

A reference numeral 21 denotes a DC motor to be a driving unit (torquegenerating source) of a valve for opening/closing an exhaust gaspassage, 22 denotes a motor case mounted on the valve body 1, 23 denotesa rotor rotatably supported in the motor case 22 via bearings 24, 25,and the rotor 23 has a screw hole 23 a made through the central portionof a shaft. A reference numeral 26 denotes a magnet mounted on the outerperipheral portion of the rotor 23, 27 denotes a stator core surroundingthe outer periphery of the magnet 26, and a predetermined gap is formedbetween this stator core 27 and the above mentioned magnet 26.

A reference numeral 28 denotes a coil arranged in the stator core 27 andconstituting a stator, 29 denotes a motor shaft to be a valve drivingshaft, and this motor shaft 29 is made in a screw shaft and screwed intothe screw hole 23 a of the above mentioned rotor 23 and moved in anaxial direction by the rotation of the above mentioned rotor 23.

A reference numeral 30 denotes a valve shaft abutting member integrallyformed with the motor shaft 29. By making the top end of a valve shaft13 having the above mentioned valve 11 at its top end abut against thetip (bottom end in FIG. 1) of this valve shaft abutting member 30, thevalve shaft 13 is made to follow a movement in an axial direction of theabove mentioned motor shaft 29 to thereby open/close the above mentionedvalve 11.

A reference numeral 31 denotes a cover mounted on an end surface on thevalve shaft abutting member 30 side in the motor case 22, 32 denotes aspring retaining member mounted on the tip side of the valve shaftabutting member 30, 33 denotes a spring hung between the springretaining member 32 and the above mentioned cover 31 for urging thevalve, and this spring 33 urges the valve 11 at the tip of the valveshaft via the valve shaft abutting member 30 in a direction that opensthe valve 11. A reference numeral 34 denotes a commutator rotatingintegrally with the rotor 23 and having a shaft hole 34 a at its centralportion.

A reference numeral 35 denotes a power source side case mounted on anopening end on the commutator 34 side of the motor case 22. This powersource side case 35 is an integrally molded part made of synthetic resinand constitutes a main body of a device for passing current through theDC motor 21 and is an integral combination of a built in sensor portion36 in which a position sensor (not shown) for detecting the opening ofthe above mentioned valve is built and an input/output connector portion37 in which a connector terminal is built.

A reference numeral 38 denotes a brush holding cylindrical portionintegrally molded with a wall opposed to the commutator 34 in the powersource side case 35, and 39 denotes a brush slidably inserted into thebrush holding cylindrical portion 38 for passing a current. This brush39 is made of carbon powder and copper powder and is connected via alead wire (not shown) to the connector terminal of the above mentionedinput/output connector portion 37.

Next, an operation will be described. Passing a current through the coil28 via the brush 39 and the commutator 34 generates a rotational torquein the rotor 23 by an interaction between a magnetic field generated bythe coil 28 and the magnetic field of the magnet 26. When the rotor 23is rotated by the rotational torque, the motor shaft 29 screwed into thescrew hole 23 a of the rotor 23 is fed by the screw and moved straightin an axial direction.

Here, in a case where the motor shaft 29 is moved downward in FIG. 1,the valve shaft abutting member 30 is pushed by the motor shaft 29 inthe direction of an urging force of the spring 33 to open the controlvalve 11 via the valve shaft 13 against which the valve shaft abuttingmember 30 abuts. Then, when the valve 11 moves near to a target positionand a difference between a present position and a target positionbecomes nearly equal to zero, an electric power required to hold thevalve 11 at its position against the restoring force of the returnspring 18 is supplied to the DC motor 21.

On the other hand, when the rotor 23 of the DC motor 21 is rotated in adirection opposite to the above mentioned direction, the motor shaft 29is moved upward in FIG. 1 and the valve shaft 13 abutting against thevalve shaft abutting member 30 integral with the motor shaft 29 followsthe motor shaft 29 by the restoring force of the return spring 18 toclose the valve.

FIG. 3 is a diagram of one example of a circuit constitution to show aservo control device for controlling the driving of the above mentionedDC motor 21. In FIG. 3, a reference numeral 41 denotes a position sensorand this position sensor 41 has a movable contact 43 moving on aresistor 42 to which a constant voltage is applied by a power supplyterminal and when the movable contact 43 moves with the rotation of therotor 23, a voltage responsive to its moving position, that is to say, avoltage in compliance with the valve position is outputted as adetection signal.

A reference 44 denotes a controller block and this controller block 44has an A/D input port 45 inputted with the detection signal from thevalve position sensor 41, a filter 46 for reading the output of the A/Dinput port 45, a PI control computing section 48 for performing a PIcontrol computation based on the output of the filter 46 and the outputof a target value determining section 47, an excitation switching andduty computing section 49 for performing an excitation duty computationbased on the output of the PI control computing section 48, a digitaloutput port 50 for outputting an ON/OFF signal based on the output ofthe excitation switching and duty computing section 49 and a PWM outputport 51 for outputting a PWM signal.

A reference numeral 52 denotes a switching circuit for controlling thepassing of a current through the DC motor 21. A (+) side end of the DCmotor 21 is connected to a connection point of semiconductor switchingdevices (hereinafter referred to as switch device) 53, 54 connected inseries and a (−) side end thereof is connected to a connection point ofsemiconductor switching devices (hereinafter referred to as switchdevice) 55, 56 connected in series.

To each of the above mentioned switch devices 53, 55 is connected eachof transistors 57, 58 which is turned ON by the output of the digitaloutput port 50, and to each of the above mentioned switch devices 54, 56is connected each of transistors 59, 60 which is turned ON/OFF by theoutput of the PWM output port 51.

Next, an operation will be described.

When a target value is determined by the target value determiningsection 47, the PI control computing section 48 performs the PI controlcomputation based on the above mentioned target value and a detectionvalue corresponding to a present valve position, which is detected bythe position sensor 41 and inputted via the A/D input port 45 and thefilter 46, and then the excitation switching and duty computing section49 performs the excitation duty computation based on this computationresult.

The digital output port 50 outputs an ON signal to a terminal (a) basedon the output of the excitation switching and duty computing section 49to bring the switch device 53 into conduction via the transistor 57 tothereby connect the (+) terminal of the DC motor 21 to a power applyingterminal V. On the other hand, the PWM output port 51 outputs a PWMsignal to an output terminal (b) based on the output of the excitationswitching and duty computing section 49 to control a conduction of theswitch device 56 via the transistor 60 to connect the (−) terminal ofthe DC motor 21 to an earth E thereby passing a current in a directionshown by a solid line.

In this manner, the DC motor 21 is operated to rotate the rotor 23, themotor shaft 29 is moved down by the rotation of its rotor 23, and bythis moving down motion the valve shaft 13 is moved in the samedirection against the return spring 18 to move the control valve 11 to atarget position to thereby open the control valve 11. Then, when thecontrol valve 11 moves near to the target position and the PI controlcomputing section 48 recognizes that a difference between a detectionvalue of a present valve position detected by the position sensor 41 andthe target value becomes nearly equal to zero, the excitation switchingand duty computing section 49 computes duty in response to the outputsignal of the PI control computing section 48 and supplies the DC motor21 with an electric power required to hold the valve 11 at its targetvalve opening position against the restoring force of the return spring18 based on this computed duty.

Since the conventional servomechanism to which a DC motor is applied isconstituted as the above mentioned way, the valve is oscillated by thefollowing causes when it performs the servo control near the targetvalve opening position.

(1) Since variations in torque are partially caused by variations in thecurrent passing through the motor, the valve as a driven body to besubjected to a feed back control is not made stable near the targetposition.

(2) When the output of the sensor is read in, if the output of thesensor is mixed with motor noises, the output of the sensor can not beread in with high accuracy, so that the valve as the driven body to becontrolled based on the output is not made stable in the vicinity of thetarget position.

There is presented a problem that the occurrence of oscillation of thevalve prevents the valve from being stopped stably at the targetposition.

The present invention has been made to solve the above mentionedproblem, and an object of the present invention is to provide a devicefor reducing the oscillation caused when a DC motor is subjected to aservo control.

DISCLOSURE OF THE INVENTION

A servo control device of a DC motor in accordance with the presentinvention includes: a DC motor for driving a driven body against arestoring force; a position sensor for detecting a moving position ofthe driven body; a speed detecting section for detecting a moving speedof the driven body based on a detection value of the position sensor; adeviation detecting section for detecting a deviation of the driven bodybased on the detection value of the position sensor; a PI controlcomputing section that receives the detected moving speed and thedetected deviation and a target value predetermined by a target valuedetermining section and performs a PI control computation; a steadyjudgment section that judges from the moving speed and the deviationwhether conditions of a steady region are held and starts the PI controlcomputing section by an output signal when the condition of the steadyregion are judged to hold to thereby make the PI control computingsection execute the PI control computation; and an excitation switchingand duty computing section for outputting a power supply control signalof the DC motor based on an output signal of the PI control computingsection.

By this arrangement it is made possible to reduce an oscillation of thevalve in a case where the valve is held in a steady region that isvicinity of a target valve opening position.

In the servo control device of a DC motor in accordance with the presentinvention, the detection value from the position sensor is read in threetimes and the second largest detection value is adopted.

By this arrangement it is made possible to input the detection value ofthe position sensor with the steep noise removed and thus to correctlyperform the servo control of the Dc motor even if noise caused by abrush part of the DC motor with a brush is introduced into the positionsensor to make steep noise and this steep noise is inputted as thedetection value of the position sensor.

A servo control device of a DC motor in accordance with the presentinvention includes: a DC motor for driving a driven body against arestoring force; a position sensor for detecting a moving position ofthe driven body; a PI control computing section that receives adetection value of the position sensor and a target value predeterminedby a target value determining section and performs a PI controlcomputation; an excitation switching and duty computing section foroutputting a power supply control signal of the DC motor based on anoutput signal of the PI control computing section; a current detectingsection for detecting current passing through the DC motor; and acontrol section for controlling the excitation switching and dutycomputing section so as to suppress a variation in the current passingthrough the DC motor based on a detection value of the current detectingsection.

By this arrangement it is made possible to suppress a variation intorque caused by an abrupt variation in the current passing through theDC motor and thus to prevent the driven body from being oscillated.

In the servo control device of a DC motor in accordance with the presentinvention, the detection value from the position sensor is read in threetimes and the second largest detection value is adopted.

By this arrangement it is made possible to input the detection value ofthe position sensor with the steep noise removed and thus to correctlyperform the servo control of the Dc motor even if noise caused by abrush part of the DC motor with a brush is introduced into the positionsensor to make steep noise and this steep noise is inputted as thedetection value of the position sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic explanatory diagram of an engine exhaust gassystem.

FIG. 2 is a longitudinal cross sectional view to show a constitution ofan EGR valve.

FIG. 3 is a control circuit diagram of a DC motor.

FIG. 4 is an opening characteristic graph of a valve.

FIG. 5 is a control circuit diagram of a DC motor in a servo controldevice of the DC motor in accordance with embodiment 1 of the presentinvention.

FIG. 6 is a waveform diagram to show a relationship of the output of aposition sensor with respect to a current passing through the motor.

FIG. 7 is a control circuit diagram of a DC motor in a servo controldevice of the DC motor in accordance with embodiment 2 of the presentinvention.

FIG. 8 is an explanatory diagram to show that an error occurs in thereading of the output of a sensor.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter in order to describe the present invention in more detail,the best mode for carrying out the invention will be described belowwith reference to the accompanied drawings.

Embodiment 1

FIG. 4 is a control characteristic graph at the time of a servo controlof a DC motor. A reference symbol A denotes a non steady region in whicha constant PI is not varied and B denotes a steady region in which theconstant PI is varied. In a judgment whether or not a region is a steadyregion, when a condition relating to a deviation of “displacement(present value−target value)<steady judgment displacement (that is avalue determined by an experiment in advance)” and a condition relatingto a speed of “speed<steady judgment speed (that is a value determinedby an experiment in advance)” are held in the region, the region isjudged to be a steady region.

FIG. 5 is a servo control circuit diagram of a DC motor to show aconstitution of embodiment 1. In FIG. 5, a reference numeral 66 denotesa speed detecting section for detecting a speed based on an output of aposition sensor 41 which is read via an A/D input port 45 and a filter46, 67 denotes a deviation detecting section for detecting a deviationbased on an output of the position sensor 41 which is read via the A/Dinput port 45 and the filter 46, 68 denotes a steady judgment sectionthat makes a judgment, based on the outputs of the speed detectingsection 66 and the deviation detecting section 67, whether or not thecondition of the steady region are held and that when it judges thecondition of the steady region are held, it makes a PI control computingsection 48 execute a PI control computation. The other constitution isthe same as the above mentioned conventional circuit constitution shownin FIG. 3, so the same parts are denoted by the same reference symbolsand their further descriptions will be omitted.

Next, an operation will be described.

When the target value determining section 47 determines a target value,the speed detecting section 66 detects a speed and the deviationdetecting section 67 detects a deviation based on the above mentionedtarget value and a detection value corresponding to a present valveposition, detected by the position sensor 41 and inputted via the A/Dinput port 45 and the filter 46, and the steady judgment section 68makes a judgment whether the condition of the steady region are heldbased on the detected speed signal and the detected deviation signal. Ina case where the condition of the steady region are not held, that is tosay in a case of a non steady region A shown in FIG. 4, the PI controlcomputing section 48 does not perform a computing action. For thisreason, the excitation switching and duty computing section 49 outputs apreviously determined duty signal to the PWM output port 51.

The digital output port 50 outputs an ON signal to a terminal (a) basedon an output of the excitation switching and duty computing section 49to bring the switch device 53 into conduction via a transistor 57 tothereby connect the (+) terminal of the DC motor 21 to the powerapplying terminal V. On the other hand, the PWM output port 51 outputs aPWM signal to the output terminal (b) based on the output of theexcitation switching and duty computing section 49 to control aconduction/non conduction of the switch device 56 via the transistor 60to connect the (−) terminal of the DC motor 21 to an earth E to therebypass a current in a direction shown by a solid line arrow.

In this manner, the DC motor 21 is rotated to move down the motor shaft29 by the rotation of its rotor 23 to move the valve shaft 13 in thesame direction against the return spring 18 by this down movementthereby moving a valve 11 to a target position to open the valve 11.Then, when the steady judgment section 68 detects that the valve 11moves near to the target position, that is to say the valve 11 entersthe steady region based on the above mentioned speed detection signaland the deviation detection signal, the PI control computing section 48is started by the steady judgment output of the steady judgment section68 to perform the PI control computation based on the speed signal fromthe speed detecting section 66 and the deviation signal from thedeviation detecting section 67 to control the excitation switching andduty computing section 49 by the output of the PI control computingsection 48 thereby to make the excitation switching and duty computingsection 49 output a signal at contracted duty intervals, for example.

As described above according to embodiment 1, the servo control detectsthat the valve 11 enters the steady judgment region of the targetposition and varies a control constant (PI value) in the steady judgmentregion to vary duty, so it is made possible to vary the PI constant suchthat the amount of control of the servo control does not varysubstantially in the steady region and thus to reduce the oscillation ofthe valve in the steady judgment region.

Embodiment 2

FIG. 6 is a diagram to show that the detection signal of the positionsensor 41, that is to say a position of the valve 11 is varied by achange in current passing through the DC motor 21, and in embodiment 2,it is intended to suppress such a variation in position of the valve 11.

FIG. 7 is a diagram to show the servo control device of a DC motorshowing the constitution of embodiment 2. In FIG. 7, a reference numeral71 denotes a current detecting section for detecting current passingthrough the DC motor 21, and the current detecting section 71 includes aresistor 72, a comparator 73, an input port and the like. A referencenumeral 75 denotes a control section of feed forward or the like forcontrolling the excitation switching and duty computing section 49 basedon a detection signal of the current detecting section 71. Then, theother constitution is the same as the constitution in the abovementioned prior art shown in FIG. 3 and the same parts are denoted bythe same reference symbols and their further descriptions will beomitted.

Next, an operation will be described.

When the valve 11 is moved in a direction that opens the valve 11 by thesame operation as described in the prior art to come near to a targetvalue and then the DC motor 21 is made to generate a driving force equalto a restoring force of the return spring 18 to hold the valve 11 at thetarget position, if the current detecting section 71 detects thatcurrent passing through the DC motor 21 is suddenly changed, then thecontrol section 75 inputted with a detection signal from the currentdetecting section 71 is made possible to control the excitationswitching and duty computing section 49 so as to suppress the variationsin the current passing through the DC motor 21 thereby preventing thevalve 11 from being oscillated by a change in the current passingthrough the DC motor 21.

As described above, according to this embodiment 2, the DC motor 21 ismade possible to generate the driving force equal to the restoring forceof the return spring 18 to hold the valve 11 at the target position and,when the current passing through the DC motor 21 is increased, thisincrease in the current is automatically reduced so it is made possibleto prevent the valve 11 from being oscillated by the increase in thecurrent.

Embodiment 3

FIG. 8 is a diagram to show the relationship between time and thedetection signal of the position sensor 41. When the detection signal ofthe position sensor 41 for detecting the moving position of the valve 11of a driven body is read in, if motor noises are added to the detectionsignal, the detection signal is varied substantially as compared withthe other detection signal to make it difficult to read a correctdetection value in. Thus, the detection signal of the position sensor 41is arranged to be read in three times and the second largest read indetection signal, for example, V1 in FIG. 8 is adopted. This mediumvalue picking up function is imparted, for example, to the A/D inputport 45 shown in FIG. 5 or FIG. 7 and the second largest read indetection value is supplied to the filter 46.

As described above according to this embodiment 3, adopting the secondlargest read-in detection signal makes it possible to exclude thedetection signal affected by noises and to read correct detection signalin and thus to perform the servo control stably.

INDUSTRIAL APPLICABILITY

As described above the servo control device of a DC motor in accordancewith the present invention is suitable for stabilizing an operation inthe servo control.

What is claimed is:
 1. A servo control device of a DC motor comprising:a DC motor for driving a driven body against a restoring force; aposition sensor for detecting a moving position of said driven body; aspeed detecting section for detecting a moving speed of said driven bodybased on a detection value of the position sensor; a deviation detectingsection for detecting a deviation of the driven body based on thedetection value of the position sensor; a PI control computing sectionthat receives the detected moving speed and the detected deviation and atarget value predetermined by a target value determining section andperforms a PI control computation; a steady judgment section that judgesfrom the moving speed and the deviation whether conditions of a steadyregion are held and starts said PI control computing section by anoutput signal when the conditions of the steady region are judged tohold to thereby make the PI control computing section execute the PIcontrol computation; and an excitation switching and duty computingsection for outputting a power supply control signal of said DC motorbased on an output signal of the PI control computing section.
 2. Theservo control device of a DC motor according to claim 1, wherein thedetection value from the position sensor is read in three times and thesecond largest detection value is adopted.
 3. A servo control device ofa DC motor comprising: a DC motor for driving a driven body against arestoring force; a position sensor for detecting a moving position ofsaid driven body; a PI control computing section that receives adetection value of the position sensor and a target value predeterminedby a target value determining section and performs a PI controlcomputation; an excitation switching and duty computing section foroutputting a power supply control signal of said DC motor based on anoutput signal of the PI control computing section; a current detectingsection for detecting current passing through said DC motor; and acontrol section for controlling the excitation switching and dutycomputing section so as to suppress a variation in said current passingthrough the DC motor based on a detection value of the current detectingsection.
 4. The servo control device of a DC motor according to claim 3,wherein the detection value from the position sensor is read in threetimes and the second largest detection value is adopted.